Haptic devices form specific man-machine interfaces. A haptic device provides, on the one hand, control and, on the other hand, tactile sensation to interaction with a technical system. A haptic device provides its user with force-feedback information on the motion and/or force input generated by the user.
Applications, for which haptic devices may be used, include robotics, tele-operation, minimal invasive surgery, simulators and computer-based games.
A characteristic of a haptic device is its force rendering capabilities when a virtual contact with a hard body is simulated. To this end, haptic devices including parallel kinematics structures, for example a so-called Delta parallel kinematics structure, are well suited. The parallel kinematics design provides for high mechanical stiffness and low mass/inertia and, thus, high static and dynamic stiffness as well as high force levels. Such haptic devices may be used, for example, as robot or manipulator for performing programmed tasks or as a haptic device where force constraints can be applied into the hands of the operator.
Another characteristic of a haptic device is transparency. Haptic transparency is a performance criteria used to quantify the fidelity with which virtual object properties are presented to and perceived by the human user through a haptic device when the user's hand is in contact therewith.
For gravity compensation, which is also referred to as static balancing, active approaches and passive approaches are known. Both approaches generate forces and/or torques in directions opposite to gravity related forces and/or torques.
In active approaches, such forces and/or torques may be generated by means of existing actuators and/or additional actuators. Using actuators already existing, the maximum force level and transparency are generally reduced due to, for example, increased friction in actuators. Further, heat dissipation and/or power consumption are usually increased. To compensate for such effects, actuators with higher power and force/torque ratings may be used, however, resulting in higher inertia and friction. Additional actuators add costs and complexity. Known approaches for gravity compensation suffer however from their complexity and/or sub-optimal results.